National averages don't accurately reflect what's going on in micro-economies like the Bay Area.
What's happening to wages in Des Moines has no bearing on what is going on here with Google, Apple, Tesla, Facebook, Oracle, Cisco, Symantec....etc.
Yes, national wages have stagnated. But the wages of young tech workers here have clearly gone up. Those people have the money to pay more for housing in SF, Peninsula, South Bay. Those people have the money to pay more for sporting entertainment options.
If you and 9 of your neighbors can't afford $5k/month in rent, but 10 new tech workers can....your landlord won't care. He'll take the people who have higher wages and can pay the higher rent, regardless of whether you personally (or some average person in Cleveland) are earning higher wages or not.
Same goes for Plattner, York, Baer, Davis, Wolffe, and Lacoub. Maybe you can't afford to pay 10% more for tickets. But they're betting someone here can, and will. And for the most part, they are right. 16k+ are still willing to pay big bucks to watch a mediocre Sharks team on a weeknight in October. If you can afford it, they'll gladly take your money. If you can't afford it, they'd rather take the money of your more affluent neighbors.
Wages and housing prices really haven't changed much in the last year or two since the Sharks were selling out every game. What has changed is that, for the first time in a decade, the Sharks weren't a playoff team. And their prospects for this season aren't significantly higher. Combine that with entertainment dollar competition from a reigning NBA championship team, and there is your attendance drop-off. If the Sharks had advanced to the WCF last year, the disposable income would magically be there.